The invention relates to a balancing apparatus for a surgical microscope, mounted on a rotation axis (A axis) that is held via a pivot support on a stand. The surgical microscope is balanceable in the Y and the Z direction via a cross-slide (alternative common designation: A-B slide) in two spatial directions (horizontal and vertical spatial direction). A typical construction in accordance with these features is the Applicant's MC1 surgical microscope. A “stand” is to be understood for purposes of the invention as any apparatus that spaces a surgical microscope away from the floor.
As is known to one skilled in the art, surgical microscopes should be very easy to move, and quickly displaceable without a great expenditure of energy. To ensure that a surgical microscope does not move on its own once a position is established, the forces and moments occurring in any position must be equalized (balanced). If the surgical microscope is not sufficiently equalized, however, brakes or bracing devices must be present in order to hold the surgical microscope in its position. Such brakes or bracing devices disadvantageously increase the overall weight of the structure. The forces and moments should be balanced out even when brakes or bracing devices are present, however, in order to enable easy movement of the surgical microscope in three dimensions when the brakes are released or the bracing devices are removed.
On the other hand, the use of a surgical microscope normally involves utilization of a wide variety of different accessories (e.g. tubes, extensions, filters, auxiliary lenses, etc.). This results in most cases, however, in a shift of the overall center of gravity. As a result, the surgical microscope is no longer in equilibrium and must be balanced out again. The basic goal in this context is to keep the overall center of gravity on the pivot axis of the surgical microscope.
DE 10133018 A1 (of the same Applicant) describes one such arrangement; here again, an optics carrier along with a surgical microscope are rotatable about a horizontal rotation axis (A axis). They need to be balanced out with reference to this A axis so that when the brakes are released, a surgeon can as easily as possible, i.e. with as little resistance and torque as possible, rotate the optics carrier (and thus the surgical microscope) about this A axis. This rotation axis is usually configured on the lower part of the pivot support and is equipped with a brake unit or locking unit that prevents any rotary movement of the optics carrier, and therefore of the surgical microscope, with reference to the pivot support.
Installed between the optics carrier and the pivot support is a balancing unit with which the optics carrier along with the surgical microscope can be balanced out about the horizontal A axis in the Y and the Z direction. This balancing unit encompasses two slides that are arranged one above another. One of them is displaceable in the Y direction and the other in the Z direction, each by means of a displacement unit, and they can be immobilized in a position that is established. Arranged at the upper end of the pivot support is a further displacement unit that enables a displacement in the X direction (FIG. 2 of DE 10133018 A1).
The solutions in accordance with DE 10133018 A1 (FIGS. 2 and 3) have not yet appeared in practical use. A similar, older approach, however, has been disclosed by the Applicant's MC1 stand. With this approach, the Y-Z displacement unit made up of the two slides arranged one above another was mounted on the rotation axis in such a way that the Z slide was mounted directly on the rotation axis, and the Y slide was mounted on the one hand directly on the Z slide and on the other hand on the optics carrier. As in the case of the construction according to FIG. 2 of DE 10133018 A1, the X slide was mounted above the pivot support. This construction has proven substantially successful. It had one disadvantage, however: In order to enable sufficient balancing for the surgeon even in those system configurations in which, for example, assistant's tubes or lateral add-on units are to be attached to the optics carrier, the surgeon must carry out another balancing procedure each time such add-on units are installed or removed. For this, once the brake or locking system of the optics carrier relative to the A axis has been released, the surgeon must                a) bring the optics carrier into a vertical position corresponding to a normal observation position of the surgical microscope; then        b) rotate the balancing screw for displacement in the Y direction until, and in directions such that, the surgical microscope is balanced across the A axis in that position; then        c) bring the optics carrier into a position that is horizontal with respect to the normal vertical observation position; then        d) rotate the balancing screw for displacement in the Z direction until, and in such directions that, the surgical microscope is once again balanced across the A axis.        
After completion of these balancing procedures, the microscope is completely balanced out with reference to the A axis, i.e. it can be pivoted across the A axis as if weightless.
The result of steps a) to d) with the above arrangement is, however, that the surgeon has his or her “hands full,” and accordingly loses a great deal of time while changing the add-on units and afterward during the balancing procedure. An additional complication is that during a surgical operation, the balancing screws are located in the area that is “draped” (covered with a drape) during a surgical operation, so that the surgeon has difficulty reaching these screws or finds it almost impossible to actuate them through the drape.
An obvious approach to eliminating this problem would be to retrofit the MC1 with an automatic balancing apparatus that independently performs at least steps b) and d). An automatic balancing system of this kind would, however, make the configuration considerably more expensive. There is moreover no reason, for this practical application, to explore whether (or how) this might be technically achievable. As an alternative, ideal balancing could be dispensed with by attaining, as with other products on the market, correct positioning in the unbalanced state with an assistance apparatus using spring force or the like. Smooth motion of the surgical microscope would, however, thereby be limited. On the other hand, homogeneity of the movements would also thereby be reduced.
The problem described above is therefore the basis of the invention as a first object. The intention is thus to achieve a reduction in or simplification of the balancing procedures without expensive and complex automation of the balancing function about the A axis.
The MC1 of the existing art also exhibited a further problem, however:
In order, however, to enable sufficient balancing for the surgeon even, and especially, in those configurations of the system in which, for example, assistant's tubes or lateral add-on units are attached, a consequence of the known arrangement according to the MC1 is that these add-on units can collide, during the balancing procedure, with the slide that sits on the A axis and is responsible for vertical displacement. The freedom of movement of the surgical microscope was therefore previously limited in the case of the known unit. On the other hand, homogeneity of the movements was thereby also reduced, since complete balancing was not always possible.
In the past, in accordance with the existing art in the context of the MC1, in order to reduce this difficulty the procedure of balancing out in the Y and Z directions was made easier by attaching an add-on weight. The add-on weight, with its mass of approximately 3.5 kg, was attached on the side of the optics carrier located opposite the surgical microscope. The add-on units were thus balanced out across the A axis at least in terms of the Y direction (with the surgical microscope in the normal position; see step a) above).
The disadvantage of this known weight compensation is that it considerably increases the total weight, which results in increased inertia when pivoting. Installation or removal of this add-on weight also required additional effort. This method is therefore time-consuming, and moreover results in increased forces and moments on the stand as a whole because of the greater total weight (see e.g. EP-0476551 A1). The add-on weight in fact produces not only an increase in torque (moment of resistance to rotation) during the displacement procedure, but also greater friction in every bearing of the entire stand, thus increasing the overall inertia of the stand and limiting its mobility. Homogeneity of the movements of the stand is also thereby reduced. In addition, the dimensions of the carrier arms of the stand (and of all other load-bearing components) of course also had to be correspondingly enlarged, which in turn considerably increased the total weight of these components and thus also the cost of the stand.
In the most up-to-date surgical practice, surgical microscopes not only need to meet standard requirements in terms of optical quality, bright illumination, compact design, and maximum flexibility, but also must incorporate additional operational aspects. Consideration must now be given, for example, to the fact that the number of surgical operations per day has risen. The time needed to set up a surgical microscope for the next operation is becoming increasingly important. As an essential component of the operating-room infrastructure, the surgical microscope has a significant influence on costly preparation time.
The second object underlying the invention is therefore that of even further improving an apparatus that has been improved in accordance with the first object, which apparatus enables relatively faster, simpler, and complete balancing of the surgical microscope without an add-on weight and which can significantly reduce or eliminate the aforementioned disadvantages of the existing art. The intention is therefore for all possible configurations of the surgical microscope to be as easy as possible for the surgeon to balance out.